Washing machines typically include a cabinet which receives a stationary tub for containing wash and rinse water. A wash basket is rotatably mounted within the wash tub. A drive assembly and a brake assembly can be positioned with respect to the wash tub and configured to rotate and control the rotation of the wash basket within the wash tub to cleanse the wash load loaded into the wash basket. Upon completion of a wash cycle, a pump assembly can be used to rinse and drain the soiled water to a draining system.
Washing machines include vertical axis washing machines and horizontal axis washing machines, where “vertical axis” and “horizontal axis” refer to the axis of rotation of a wash basket in the washing machine. Horizontal axis washing machines typically have the wash tub suspended in the cabinet by simple spring assemblies and damped from below using various damping devices. Horizontal axis washers exhibit many vibration harmonics and work in a wide range of rotational speeds. Vibration in horizontal axis washers has been addressed through use of external feedback, such as through use of variable speeds based on accelerometer feedback or by motor feedback to control rebalance. Vibration has also been addressed through use of fixed friction damping devices, tuned to one condition. Fixed friction type damping devices, however, cannot accommodate the infinite range of mass, imbalance, and rotational speed seen in horizontal axis washing machines.
Thus a need exists for a damping device with self-regulating damping characteristics that will adapt to the needs of the washing machine without external feedback within the washing machine from other devices. A damping device that will provide an increased damping ratio when the amplitude of displacement is increased and that will provide reduced damping at low displacements would be particularly useful.